The femur or thigh bone is the longest, largest, and strongest bone of the body. Proximally, the femur has a spherical head (the femoral head) that articulates with the pelvis to form the hip joint. The femoral head is connected to the body of the femur (the femoral body) by a neck that extends obliquely from the body of the femur, such that the femoral head is disposed medially and superiorly to the femoral body. Distally, the femur forms a pair of femoral condyles that articulate with the tibia to form medial and lateral compartments of the knee joint.
Fractures of the femur may be treated using various procedures, determined in part by the nature of the fracture. Segmental fractures of the femur, that is, two or more fractures in the shaft of the femur that create a fracture-bounded segment, are often fixed with an intramedullary nail disposed longitudinally in the medullary canal of the femur. The nail may be secured to the femur on opposing sides of the fracture-bounded segment using fasteners, such as bone screws, to fix the fractured femur.
In contrast to segmental fractures, fractures near either end of the femur may be more difficult to fix because the attached muscles tend to pull bone fragments in non-longitudinal directions. For example, femoral hip fractures (“pertrochanteric fractures”) may extend obliquely and/or longitudinally near and/or through the greater and/or lesser trochanters of the proximal femur, to separate the femoral head from the femoral body. Many pertrochanteric fractures are also characterized as intertrochanteric fractures that involve one (“stable” intertrochanteric fractures) or both (“unstable” intertrochanteric fractures) trochanters of the femur. Hip fractures are a common orthopedic injury. For example, in the United States, 250,000 hip fractures occur each year. This number may double or triple by the year 2050.
Surgical installation of an orthopedic implant for internal fixation is the treatment of choice for virtually all hip fractures. For example, a large screw coupled obliquely to a bone plate (termed a sliding or compression hip screw) has been used for years to stabilize intertrochanteric fractures. However, there is dissatisfaction with the sliding hip screw because of the loss of reduction that can occur and also because of the extent of soft tissue dissection necessary to install the device.
An increasingly popular, alternative approach to fixation of intertrochanteric hip fractures involves an intramedullary nail coupled to a lag screw. However, in many cases the outcome is unsatisfactory. For example, the lag screw may protrude laterally from the femoral shaft during fracture settling. In addition, a large hole is created in the greater trochanter for receiving the lag screw, which may damage insertion of the abductor muscles necessary for proper hip function. Furthermore, lag screws may exhibit a Z-effect phenomenon, in which the lag screws migrate in opposite directions during physiologic loading. The Z-effect phenomenon may be most common with nail-based fixation devices that incorporate a lag screw sliding within a barrel.
More effective and/or less expensive methods and devices for fixing pertrochanteric fractures and other fractures near the end of the femur are needed. The methods and devices should sufficiently stabilize the fractured femur to limit collapse of pertrochanteric fractures that extend obliquely and/or longitudinally.